Storage elements employing bipolar programmable resistance materials offer a potential replacement for current non-volatile memory, including, but not limited to, flash memory, one-transistor one-capacitor (1T1C) dynamic random access memory (DRAM) and static random access memory (SRAM). Memory devices employing bipolar programmable resistance storage elements typically rely on a reversal of the polarity of a voltage applied across the storage element in each of the devices in order to write the respective logic states of the memory devices. These nonvolatile bipolar programmable resistance storage elements, which include materials such as “spin-switched” or “spin momentum transfer” magnetic materials and/or programmable resistance transition-metal oxides, can be programmed at low voltages (e.g., less than about 1.5 volts (V)) and can achieve a high performance comparable to DRAM or SRAM and superior to flash memory.
Due to the bipolar nature of the programmable resistance storage element, in a one-transistor one programmable resistor (1T1R) memory cell configuration, each memory cell will typically require an intervening erase operation, which involves the use of negative voltages, before a write operation is performed. This intervening erase operation undesirably increases the complexity of circuits that are peripheral to the memory device in order to support the generation of the negative voltages employed, and is therefore an impediment to achieving higher performance in the memory device. Although, a direct write without the intervening erase operation can be achieved by providing dual select lines in a bit direction, this approach would significantly increase a size of the memory cell in order to accommodate the additional select lines. Consequently, the cost of the memory cell, which is directly proportional to memory cell size, would increase accordingly. Thus, it is of utmost importance to minimize the size and complexity of the memory cell.
Accordingly, there exists a need for a nonvolatile memory architecture employing bipolar programmable resistance storage elements that does not suffer from one or more of the problems exhibited by conventional memory devices having bipolar programmable storage elements.